Acyclic Nucleoside Phosphonates Bearing (R)‐ or (S)‐9‐[3‐Hydroxy‐2‐(phosphonoethoxy)propyl] (HPEP) Moiety as Monomers for the Synthesis of Modified Oligonucleotides.

Suitably protected (R)‐ and (S)‐HPEP {9‐[3‐hydroxy‐2‐(phosphonoethoxy)propyl]} derivatives containing adenine and thymine nucleobases were prepared as monomers for the introduction of acyclic nucleotide units into oligonucleotides. The solid phase synthesis of a series of ribo and 2′‐deoxyribo nonamers containing (R)‐HPEP and (S)‐HPEP units was successfully performed in both 5′ → 3′ and 3′ → 5′ directions. The measurement of thermal characteristics of the complexes of modified nonamers with complementary DNA and RNA strands revealed a general destabilizing effect of the introduced acyclic units on the thermal stability, but in several cases [modif.RNA*RNA and modif.DNA*RNA with (S)‐HPEPA units], the duplexes were characterized in terms of Tm values. A solid‐phase synthesis afforded a series of ribo and 2′‐deoxyribo nonamers containing acyclic nucleotide units. A general destabilizing effect of the introduced acyclic units on the thermal stability of complexes of modified nonamers with the complementary DNA and RNA strands was observed, but in cases with (S)‐HPEPA units, the duplexes were characterized in terms of Tm values. [ABSTRACT FROM AUTHOR]